1. Field
One embodiment of the invention relates to an electronic device equipped with a touch sensor which serves as an operation section to instruct various types of processes.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Publication No. 2003-134210 discloses a mobile telephone device in which a wide range of the illuminated portion is lighted by one light emitting diode. This mobile telephone device includes a rear case which makes a part of the outer frame, a illuminated portion made of an opal acryl resin and provided on a part of the rear case, a light-emitting diode which lights the illuminated portion, a printed circuit board having an opening portion, in which the light-emitting diode is mounted, a diffusion sheet provided between the illuminated portion and the light-emitting diode, and a reflection sheet provided to correspond to the opening portion of the printed circuit board. The diffusion sheet is provided to diffuse the light of the light-emitting diode, thereby enhancing the light diffusion effect in the illuminated portion. The reflection sheet is provided at a position opposing the diffusion sheet.
In this mobile telephone, the light-emitting diode emits light when a telephone call is received or a mail is received. Part of the light emitted is diffused by the diffusion sheet and irradiated to the illuminated portion. Further, of the light irradiated from the light-emitting diode, the portion irradiated in the direction along the printed circuit board reflects on the diffusion sheet and is irradiated to the opposite side of the printed circuit board through the opening. This portion of the light reflects on the reflection sheet and transmits the diffusion sheet again through the opening to be irradiated to the illuminated portion. With this structure, the portion of the light leaking in the direction along the printed circuit board can be reflected as well on the diffusion sheet by the reflection board, and thus the light can be efficiently used.
However, the light irradiated in the direction along the printed circuit board is weak from the beginning; therefore when this weak light is reflected on the reflection plate and further diffused by the diffusion sheet, the light in some cases does not reach the surface of the illuminated portion as a practical phenomenon. As a result, the outer circumferential section of the illuminated portion may become dark as an impression to eyes. In order to instantly solve this problem, it is considered to increase the current supplied to the light-emitting diode. However, the increase in the current creates another problem of increasing the power consumption.